It's important to be aware of security. The older "legacy" Linux 3.4 kernels provided by Allwinner have known vulnerabilities. For example, CVE-2016-10225 describes a vulnerability in the sunxi-debug driver that could allow local users to gain root privileges.
A simpler approach is to use an SD card to boot a different OS. Allwinner H3 Firmware
Yes, the seek values matter. Sector 8 is the boot0 location. It's important to be aware of security
Typically, Allwinner chips look for a bootloader on the SD card before trying internal storage. Newer H3 chips support booting from the 128KB offset, which is safer for modern GPT partition tables. A simpler approach is to use an SD
The search for a "solid paper" on Allwinner H3 firmware yields several authoritative technical resources and guides rather than a single academic "white paper." The most comprehensive technical documentation is maintained by the linux-sunxi community
Connect a high-quality (Class 10 or UHS-1) MicroSD card to your PC.
The next time you dd an image to an SD card and see that green LED blink to life, remember: You just witnessed a 7-year-old Chinese ARM chip execute a miracle of modern firmware hacking.